Locking mechanisms for sash windows are known in which, in the closed position, the handle of the locking mechanism engages a receiving element affixed to the adjacent rail of the other window sash. Whilst such an arrangement is effective in maintaining the window closed, there is no provision for securely holding the window in an open position, i.e. if the lower sash is slid upwards, there is no positive locking means to prevent the sash sliding back down under the force of gravity.
To overcome this problem, locking mechanisms have been developed in which engagement bolts arranged at the ends of the transverse sash rail on the locking mechanism are forced into contact with a region of the frame which surrounds the sash window assembly, thereby hindering movement of the lower sash. Such an arrangement has the disadvantages that, on the one hand, the contact region wears after a period of use and so the lower sash is no longer securely held and, on the other hand, that a two-handed operation of the locking mechanism is required.
A major disadvantage with sash type windows is the difficulty in obtaining a satisfactory seal between the frames of the sashes themselves and the window frame when the window is in its closed position. Such a seal is important to prevent draughts. Thus, it is an object of the present invention to provide a locking mechanism for sash windows in which a better seal is obtained when the window is in its closed position, and which can be operated with one hand.